RT-Thread RTOS
An open source embedded real-time operating system
PCI and device tree

PCI Open Firmware integration

Implementation: **components/drivers/pci/ofw.c**. Requires **RT_USING_OFW**.

Host controllers probe as platform devices; this file connects enumerated **rt_pci_device** instances to DT **ranges** and INTx routing.

INTx: <tt>pci_ofw_irq_parse</tt>

Resolves legacy PCI INTx:

  1. Device node has **interrupts** → **rt_ofw_parse_irq_cells**
  2. Else read **INTPIN** from config; **pin == 0** → **-RT_ENOSYS**
  3. Walk bus tree:
    • Device-local **interrupt-map** if present
    • Else P2P bridge or host bridge node → **rt_ofw_parse_irq_map** with key:
map_addr[0] = (bus->number << 16) | (devfn << 8)
map_addr[3] = swizzled INTx pin /* rt_pci_irq_intx */

Missing **interrupt-map** on root → **-RT_EEMPTY** (logged).

<tt>rt_pci_ofw_irq_parse_and_map</tt>

int rt_pci_ofw_irq_parse_and_map(struct rt_pci_device *pdev,
rt_uint8_t slot, rt_uint8_t pin);

Calls **pci_ofw_irq_parse**, then **rt_ofw_map_irq**. Sets **pdev->intx_pic** from **rt_ofw_data(irq_args.data)**.

Host bridge may wire **host_bridge->irq_map** to this helper during init.

<tt>ranges</tt> parsing

**pci_ofw_parse_ranges** / **rt_pci_ofw_parse_ranges**:

  • Decodes PCI address **space_code** (config / I/O / 32-bit mem / 64-bit mem)
  • Fills **host_bridge->bus_regions**: CPU phys, PCI bus addr, size, prefetch flags
  • Used before **rt_pci_region_setup**

**rt_pci_ofw_host_bridge_init**, **rt_pci_ofw_bus_init**, **rt_pci_ofw_device_init** — per-node OFW hooks during probe.

DT artifacts

Property Use
Host **compatible** Select host driver (PCI host controllers)
**reg** ECAM MMIO
**ranges / dma-ranges** MEM/IO windows
**interrupt-map / interrupt-map-mask** INTx → PIC
Endpoint **reg** (optional) Direct **interrupts** on slot

BAR values still come from config space after enumeration.

MSI/MSI-X

MSI message address/data from PIC (**pdev->msi_pic**), not **interrupts** cells. Ensure PIC/MSI parent in DT matches host setup (PCI MSI and MSI-X).

Pitfalls

Issue Mitigation
Missing root **interrupt-map** Use MSI or fix DTS
Wrong swizzling Use **rt_pci_irq_intx** for map key
Empty **ranges** BAR assignment fails

See also